A Measurement of the Primordial Power Spectrum from Maxima and Boomerang Data

Model-independent measurements of the primordial power spectrum of matter density fluctuations provide a unique probe of physics in the very early universe, and can provide powerful constraints on inflationary models. We parametrize the primordial power spectrum $A_s^2(k)$ as an arbitrary function, and measure its binned amplitude from the cosmic microwave background radiation anisotropy (CMB) data from Maxima and Boomerang. We find that for a flat universe with $A_s^2(k)=1$ (scale-invariant) for scales $k<0.001 $h/Mpc, the primordial power spectrum deviates significantly from a scale-invariant Harrison-Zeldovich spectrum. It has a drop in power at $0.001 h/{Mpc} \la k \la 0.01 h/{Mpc}$, and a rise in power at $0.01 h/{Mpc} \la k \la 0.1 h/{Mpc}$, with the general trend of less power on small scales compared to a scale-invariant power spectrum. Our results are consistent with large scale structure data, and seem to suggest that unusual physics may have occurred in the very early universe.